Currently I am trying to solve a problem consisting of a compressible gas flow through an orifice. I am using rhoSimpleFoam for this simulation and has been struggling with this solver for weeks now.

My problem definitely does not lie with the relaxation factors as discussed in quite a few threads in this forum because adjusting this only varies when the solution blows up.

I have also tested the simulation with different solvers like rhoPisoFoam etc with no success.

After a thorough scan a my most recent blow-up a realised that it is temperature related. As soon as it reaches 0C it blows up because the thermophysical values can not be computed. The weird thing for me is that the temperature is not suppose to vary to much, but in my simulation is varies consideribly where the velocities are the highest. For all my simulations I have used the following thermoType:

I wonder what the results were in this case. Were they true to analytical solutions such as calculated from ISO 5167-2?

I am trying to do the same. While the simulations don't blow up, they definitely give results strongly differing from the ISO-solution.

For comparison reasons I use a case which at no point reaches Ma > 0.25, so incompressible treatment should be okay as well. Indeed simpleFoam does provide me with a result that does fit the ISO-solution quite well (12 % of difference for the pressure difference, qualitative very similar flow field).
Using the same case with rhoSimpleFoam nevertheless gives results which are quite off for the pressure difference (ca. 20 to 25%) and by no way does agree qualitatively with the flow field.

The mesh used was identical for both cases, simpleFoam and rhoSimpleFoam.

Attached you can see the velocity magnitude fields for both simulations.
Among other things the flow profile should become normal again after some way. It does that for simpleFoam, while rhoSimpleFoam keeps this strange kind of layering...